CC BY
17y^K 620.9
T. Koubsky, L. Kalvoda, M. Drab
Czech Technical University, Faculty of Nuclear Research and Physical Engineering, Department of Solid State Engineering, Czech Republic, Prague
AB-INITIO SIMULATION OF CHEMICAL STABILITY OF THE BIS-DGA-TYPE MOLECULE
AND ITS DEGRADATION PRODUCTS*
For the high level nuclear waste reprocessing during the DIAMEX process (DIAMide coEXtraction of the trivalent actinides and lanthanides) the bis-DGA organic compounds are being used. It is necessary to demonstrate the stability of the extractants. The chemical stability of the m-xylylene-bis-diglycolamide (compound 1) against an electrophilic attack was simulated by the chosen ab-initio computational methods (DFT). The ether oxygen atom appeared to be the weakest point. The degradation fragment 3 appeared to be more stable and together with the good extraction properties it could be developed as a new efficient extractant. This interpretation was made mainly on the base of HOMO-orbital localization. The results were in agreement with the experiment.
One of the strategies used for spent nuclear fuel management is the hydrometallurgical treatment of the high level liquid nuclear waste. Among others, it comprises the trivalent actinide and lanthanide group separation (DIAMEX process - DIAMide Extraction). In this process the compound 1 (m-xylylene-bis-diglycolamide -fig. 1) is being used for the good selective properties of its diglycolamide (DGA) group. The degradation of 1 leads clearly to undesirable effects caused by decrease of the extractant's concentration. Unlike the other fragments, the major degradation product 3 (the notation of the molecules was adopted from [1], see fig. 2) also acts as an efficient extractant, but its stability against the hydrolysis is higher.
The degradation is mainly caused by the electrophilic attack of the acidic H+ ions (the process takes place in the solution of the HNO3). The concentration of the H+ ions is increased by the radiolytic dissociation of the HNO3.
As was concluded in [2], the prevalent hydrolysis leading to 3 takes place on the ether groups. Therefore our purpose was to simulate the stability of the ether atoms of 1 and 3 against the electrophilic attack and find the differences, as was observed experimentally [1]. As a reference molecule (the structure similar to 3 together with the low stability similar to 1), the fragment 10 has been chosen (see the fig. 3).
As for the methods, the density functional theory (DFT) based software modules DMol3 (numerical basis set DNP 3.5) and Gaussian (Gaussian basis set 6-31G) with the exchange-correlation functionals PBE, RPBE, BLYP were used. As the chemical stability indicators the electrostatic potantial (ESP), Mullikan population analysis (MPA) atomic hcarges, Fukui function and the highest occupied molecular orbital (HOMO) spatial location were
calculated. The reactivity of the ether oxygen atom of 1 can be clearly seen from the volumetric data of ESP, the interpretation of the stability differences were made mainly on the basis of the spatial localization and delocalization of the HOMO.
Since the HOMO expresses the location of the highest-energy electron, in the case of donor-type reaction, this is the most reactive electron.
Hence the localized HOMO shows the high preference of reactivity of the concerned area, and on the other hand, the delocalization of the HOMO decreases the preference of reactivity and therefore refers to the higher stability of the concerned system. As for the molecule 1, the HOMO is localized in the area of amide nitrogen and ether oxygen atoms (fig. 4; the arrow points at the ether group). In the contrary, the HOMO of 3 (fig. 5) is higly delocalized over the whole molecule. This refers to the high reactivity of 1 and higher stability of 3.
For the comparison, the HOMO of 10 (fig. 6) is again localized in the same manner as for 1, which refers to the low stability. All the mentioned results are in agreement with the experimental results of the stability published in [1]. The stable fragment 3 could be developed as a new efficient extractant in the DIAMEX process thanks to its stability and favourable extraction properties.
Reference
1. Galán H., Murillo M. T., Sedano R., Núñez A., de Mendoza J., González-Espartero A., Prados Hydrolysis and Radiation Stability of m-Xylylene Bis-diglycolamide: Synthesis and Quantitative Study of Degradation Products by HPLC-APCI+ // European Journal of Organic Chemistry. 2011: n/a. doi: 10.1002/ejoc.201100443.
* The ab-initio calculations were performed with the DMol (Accelrys Software Inc.) program and Gaussian software (Frisch M. J. et al.), graphical displays were generated with Materials Studio. The work has been performed within the European project ACSEPT.
Решетневскце чтения
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Т. Коубски, Л. Калвода, М. Драб
Чешский технический университет, факультет ядерной и прикладной физики, кафедра прикладной физики твердого тела, Чешская республика, Прага
НАЧАЛЬНОЕ МОДЕЛИРОВАНИЕ ХИМИЧЕСКОЙ СТАБИЛЬНОСТИ МОЛЕКУЛ ТИПА 2-БОЛ И ПРОДУКТОВ ИХ РАСПАДА
Для высокоуровневой переработки ядерных отходов в процессе Б1ЛМЕХ (диамидной экстракции трехвалентных актинидов и лантанидов) используются органические 2-БОЛ соединения, необходимые для демонстрации стабильности экстрагентов. Химическая стабильность м-ксилилен-2-дигликольамида (соединение 1) к электрофилическому воздействию была смоделирована путем выбора начальных вычислительных методов (БЕТ). Самым слабым оказался эфирный атом кислорода. Третий фрагмент распада оказался более стабильным и вместе с хорошими экстракционными свойствами может быть усовершенствован до нового эффективного экстрагента. Такая интерпретация была сделана в основном на базе НОМО-орбитальной локализации. Теоретические результаты совпали с экспериментом.
© КотЛ^ку Т., Ка1уо<!а Ь., БгаЪ М., 2012
